This invention relates to a shear-resisting assembly, and a shear-resisting construction unit, in which a moment-resisting strap is attached to an elongated structural member subject to moment and shear forces. A typical use for the strap would be in a shear-resisting assembly such as a post attached to a foundation, or in a shear-resisting construction unit used in a building wall attached to a foundation, or it could simply be used for attachment of another structural wood member to a relatively immovable structure.
A recent development in the building industry, particularly for framed homes of either wood or metal, or for light commercial or apartment buildings is the use of prefabricated shear-resisting construction units in walls for resisting lateral forces imposed on the building. An example of one such shear-resisting construction unit used in walls is described in U.S. patent application Ser. No. 08/975,940 filed Nov. 21, 1997. A commercial embodiment of a similar shear resisting construction unit used in walls is illustrated in a brochure published by Simpson Strong-Tie Company, Inc. entitled xe2x80x9cStrong-Wall(trademark) Shearwallxe2x80x9d and having a designator F-SW16HD May 1999 exp. June 2000 and bearing a copyright notice dated 1999. These shear-resisting construction units used as prefabricated components for walls provided a major step forward in providing consistent lateral resistance in buildings in the light frame industry.
Applicant found, however that such shear-resisting construction units could be greatly strengthened at little increase in cost, weight, and installation time by installing a moment-resisting strap at a crucial location in the structure in combination with a holdown connector and joined by adhesive or fastener elements such as wood screws.
The strengthened construction unit results from a composite effect in which the moment-resisting strap acts in combination with other elements to give a far greater resistance to shear and moment forces than would have been possible had the elements acted alone instead of compositely together.
The theory of the operation of these elements is further described in the specification under the headings xe2x80x9cOperation of the Moment-resisting Elongated Strap in the First Shear Resisting-assembly; xe2x80x9cOperation of the First and Second Moment-resisting elongated straps in the Shear-resisting Construction Unitxe2x80x9d, and xe2x80x9cComposite Effectxe2x80x9d.
A further enhancement effect occurs when the screws are used in sufficient number and in sufficiently close spacing to literally stitch substantially the entire back of the holdown to the moment-resisting strap and to a substantial portion of the wood structure so that a shear-resisting assembly of substantial length is stiffened and acts as a stiffened unit to transmit bending moments from the elongated wood structure to the foundation. Such a unit is extremely effective in reducing premature failure in the wood structural member due to bending. The moment resisting elongated strap extends to or slightly beyond the lower extremity of the holdown. The stitching effect of the multiple screws causes the holdown, a substantial portion of the moment resisting elongated strap, and a substantial portion of the elongated wood structure to act as a stiffened unit in resisting bending.